This invention is directed to an antenna and a system for outputting a signal to program a passive transponder, and in particular, to an antenna for transmitting a signal to a passive transponder and receiving the signal transmitted back by the passive transponder when the transponder is shielded.
Transponder and scanner systems are well known in the art. By way of example, U.S. Pat. No. 5,250,944 discloses a system for receiving a signal from a passive transponder which includes a probe for transmitting an exciter signal having a first frequency and receiving a signal from the transponder having a second frequency. The probe includes an antenna including an exciter coil for transmitting the exciter signal. The exciter coil includes a second coil and primary coil wound about the second coil. The second coil is tuned to resonate at the first frequency. A receiver is provided for driving the primary coil at the first frequency. This system has been satisfactory, however it suffers from the deficiency that it is unable to accurately send and receive signals from a passive transponder located within a partially shielded housing such as a steel cannula utilized in tagging animals.
Passive transponders are widely used to identify animals, either as part of a livestock herd, domestic pets, or for use in laboratory experiments. A convenient way for attaching the passive transponder to the animal to inject the transponder subcutaneously into the animal utilizing a cannula. To prevent infection to the animal, the cannula and transponder are sterilized and shipped to the user as a sterilized package, the transponder being stored in an ejection ready position within the cannula. The cannula must be made of FDA approved materials such as stainless steel because of the contact with the animal tissue. Stainless steel acts as a shield to the magnetic waves which are used to program passive transponders. As a result, the transponder cannot be accurately programmed or read while in the cannula. Therefore, the prior art exciter antennas are only able to program the transponder either before the transponder is placed in the cannula or after the transponder has been ejected from the cannula into the host animal. As a result, the transponder cannot be programmed and checked prior to insertion within the animal. As a result, the user who is implanting transponders into a large number of animals cannot quickly program each of the transponders prior to insertion, rather, the user must insert the transponder within the animal then program the transponder and scan the transponder as a check for proper programming. This is a time consuming process which provides no final quality control immediately prior to insertion. Therefore, an efficient system capable of transmitting a signal for programming a transponder and receiving a signal for reading the programmed transponder while the transponder is within a partially shielded environment is provided by the instant invention.